1. FIELD OF THE INVENTION
The present invention relates to a light source device for use in a color copying machine in which a light bundle is generated by the light source device toward an original document and in which a color-separation of the reflection light reflected by the original document is performed, thereby applying the color-separated light to a photo-sensitive member so as to form a color image.
DESCRIPTION OF THE PRIOR ART
In recent years, in various kinds of copying machines adopting an electro-photographic method, there is a kind of copying machine capable of forming a full color image. A full color image is formed in a manner as follows.
First, a reflection light reflected by an original document is applied to an optical color-separation filter through which a spectrum of a blue wavelength band is passed and projected onto a photo-sensitive member so as to form an electrostatic latent image. Subsequently, yellow toner is made adhere onto the electrostatic latent image and then the yellow toner adhering image is transferred to a transfer charger. Similarly, the reflection light reflected by the original document is applied to an optical color-separation filter through which a spectrum of a green wavelength is passed and projected onto the photosensitive member so as to form an electrostatic latent image, so that a magenta toner adhering image is formed to be transferred onto the yellow toner adhering image. Moreover, the reflection light reflected by the original document is applied to an optical color-separation filter through which a spectrum of a red wavelength is passed, so that a cyanic toner adhering image is formed to be transferred onto the yellow and magenta toner images. By these processes mentioned above, there is formed a compound image with yellow, magenta and cyanic toners, i.e., a full color image is formed on the transfer charger.
When a full color image is formed, the densities of the chromaticities of the three kinds of toner images with yellow, magenta and cyanic toners should be made regular and constant in order to prevent occurrence of a specific irregular coloration in the image to be formed. In other words, when an original document with the same density of the chromaticities of blue, green and red is copied, the density of the chromaticities of the three primary colors of the image to be formed should be made regular as those of the original document. However, in practical use, the above mentioned densities of the chromaticities of the three primary colors of the image to be formed are not made regular owing mainly to a spectral distribution of a light intensity generated by a light source and to a spectral sensitivity of the photosensitive member.
FIG. 1 shows a distribution of spectral intensities of a light emitted by a halogen tungsten lamp which is generally used as a light source lamp in a copying machine. As shown in FIG. 1, the distribution of the spectral intensities (relative energy ratio) of the light emitted by the halogen tungsten lamp of the light source becomes lower to higher as the wavelength band of the spectrum goes from the blue short spectrum to the red long spectrum.
FIG. 2 shows a distribution of spectral sensitivities of the photo-sensitive member provided in the copying machine, wherein the spectral sensitivities become highest at the green wavelength band and become lower in the ranges of the blue and red wavelength bands. Therefore, when an original document is copied to form an image thereof by a copying machine using the light source lamp and photo-sensitive member as mentioned above, the density of the chromaticity of the yellow toner image becomes rather higher compared to those of the magenta and cyanic toner images, and therefore, there has been a problem that the whole part of the image to be formed becomes rather yellow colored.
Therefore, there have been made various kinds of devices in order to increase the quantity of the spectral intensity of the blue wavelength band of the light emitted by the light source lamp in the prior art. For example, (1) there is employed a color-separation filter with high permeability for a spectrum of a blue wavelength band, (2) there is employed a color-separation filter permeable for a spectrum of a wavelength band shifted to rather a longer wavelength, (3) there are provided a plurality of light source lamps, (4) there is used a light source lamp with high efficiency (herein "lamp efficiency" means a ratio between a light energy and a consumed electric power of a lamp (lm/W)), and (5) power supply for a light source lamp is increased, whereby the quantity of the spectral intensity of a blue wavelength band of the light is increased.
However, the methods (1) to (5) mentioned above have faults respectively as follows.
(1) There is a limit (90% degree) for increasing the permeability of the light permeable filter, and therefore, it is impossible to perform a sufficient color correction. PA1 (2) The reproductivity of the yellow and green colors of a document becomes worse because of the shift of the permeable wavelength band of the filter. PA1 (3) The temperature inside the copying machine rises. PA1 (4) The life of the light source lamp with high efficiency is reduced. PA1 (5) Since the consumption power available in the entire parts of the copying machine is predetermined, a large increment of the consumption power can not be attained.